The actuating device of known machine tools of the above type normally comprises a first straight slideway along which runs a first powered slide supporting a second straight slideway, the projection of which on a plane forms an angle of other than zero with the projection of the first slideway on the same plane. The actuating device also comprises a second slide mounted to run along the second slideway and supporting a third slideway perpendicular to the first and second slideways and supporting a third powered slide in turn supporting the toolhead and the relevant tool.
Known machine tools of the above type have the drawback of being fairly bulky. That is, the length of each slideway is determined by the size of the relative slide in the direction of the slideway, plus the travel of the slide, plus the length of two telescopic guards located on opposite sides of the slide to protect the slideway, so that the linear size of the slideways and slides as a whole for moving the tool in the travel volume is at least twice the amount of travel permitted.
Moreover, the structure of the straight slideways is complicated by the presence of mechanical stops or bumpers for arresting the slides and preventing them from running off the slideways in the event of improper operation of the slides, and the strength of which is directly proportional to the travelling speed of the slides.
Finally, moving the tool in the travel volume using translating slides calls for moving the slides continually back and forth along the relative slideways, thus resulting in severe inertia, which severely impairs the accuracy of the machine tool unless provision is made for a fairly rigid, heavy frame, which is therefore also fairly bulky and expensive to produce, install and assemble.
It is an object of the present invention to provide a machine tool of the above type designed to eliminate at least in part the aforementioned drawbacks.
According to the present invention, there is provided a machine tool comprising a supporting frame; an operating unit fitted movably to said frame; and an actuating device for moving said operating unit with respect to said frame and parallel to a given plane; characterised in that said actuating device comprises a main electric motor in turn comprising a main stator integral with said frame, and a main rotor fitted to the main stator and rotating about a main axis with respect to the main stator; and at least one secondary electric motor in turn comprising a secondary stator integral with said main rotor, and a secondary rotor fitted to the secondary stator and rotating about a secondary axis movable with said main rotor; said main axis and said secondary axis being perpendicular to said plane, and being separated from each other by a first given distance of other than zero; said operating unit being supported eccentrically by said secondary rotor; and said first distance being less than a radius of the main rotor.
In a preferred embodiment, comprising a fixed worktable; a fixed supporting frame; at least one toolhead fitted movably to said frame; a tool mounted on said toolhead; and an actuating device for moving said tool with respect to said frame and said worktable along a machining path extending within a predetermined volume; said actuating device comprising a main electric motor in turn comprising a main stator integral with said frame, and a main rotor fitted to the main stator and rotating about a main axis, coaxial with said cylindrical volume, with respect to the main stator; at least one secondary electric motor in turn comprising a secondary stator integral with said main rotor, and a secondary rotor fitted to the secondary stator and rotating about a secondary axis movable with said main rotor; and at least a machining unit comprising straight guide means supported eccentrically by said secondary rotor, and powered slide means angularly fixed in relation to said straight guide means and movable therealong in a direction parallel to said main axis and said secondary axis; said toolhead being mounted on said powered slide means for rotation in relation thereto about a tertiary axis parallel to said main axis and said secondary axis, and each said axis being separated from each of the other axes by distances, each of which is less than a radius of the main rotor.